Zoonotic Diseases

Zoonotic diseases refers to infectious diseases transmitted naturally between animals and man.They represent a major public health problem as humans are closely in contact with animals on various fronts.


History and Emergence

Zoonotic diseases have had a tremendous impact on the evolution of civilizations where humans were closely associated with animals for domestic purposes.Zoonoses can transcend natural boundaries.Some diseases such as HIV started as a zoonotic infection but later mutated into human-only strains.Some of these diseases have caused major outbreaks some evolving into epidemics like avian influenza while others creating pandemics such as the novel coronavirus that caused COVID19.



Who is at risk?

Zoonotic pathogens can spread to humans through contact and this includes domestic and wild animals.People living adjacent to wilderness regions are at high risk for zoonoses from animals like rats,bats,racoons etc.Markets selling meat of wild animals are always a reservoir of infections as we can recall how COVID originated in the Wuhan province of China in 2019.Furthermore,the risk of contact of humans with wild animals have increased tremendously following destruction of natural habitats as part of industrialisation.


Some common Zoonotic diseases of public importance

There are umpteen zoonotic diseases,a description of which is very exhaustive and beyond the scope of this discussion.Here I would touch upon the most common zoonoses of significance to public health which are as follows:

  • Rabies

  • Anthrax

  • Leptospirosis

  • Plague

  • Yellow Fever

  • Influenza

  • Emerging Coronaviruses

  • Hydatid disease

Rabies

Rabies is perhaps one of the major zoonotic diseases of concern in view of nearly 100% mortality once infected.Dogs are the principal reservoirs of the virus whereas other animals such as foxes,bats and monkeys have also been implicated.Rabies is one of the most painful diseases which throws an infected man between intense thirst of water and fear of water at the same time.Till date,there is no cure and prophylaxis with vaccination once a suspicious exposure occurs is the only hope.

Rabies has been discussed in detail in another blogpost and you can read it at : https://www.scalpelstrokes.com/post/dogs-are-cute-but-dogbites


Anthrax

Anthrax is a bacterial zoonotic disease which usually affects farm animal like cows and sheep but can be transmitted to humans once in contact with infected materials from these animals.It is an agent of bioterrorism and naturally people who work in labs having the virus specimen are at high risk. It has also been noted in IV drug abusers notably heroin.Direct person-to-person transmission is rare.

Historically important,anthrax was the first disease in which the causative agent was definitely demonstrated as a specific micrrorganism back in 1863.

Anthrax is a seasonal disease and more common in agriculture predominant regions such as South and Central Americs,Middle East,Asia and Africa.In India,outbreaks have been reported in Mysore(1999),West Bengal(2000) and Orissa(2004-05).

Antibiotics,notably Penicillin is very effective if initiated early after diagnosis.


Leptospirosis

Leptospirosis is primarily a contagious disease of animals but occasionally communicable to humans when exposed to the pathogen through the infected secretions of animals ,mainly urine. It is a common cause of acute renal failure and outbreaks have been documented many a times across India over the past two decades.

You can read in detail about leptospiros in my blogpost at: https://www.scalpelstrokes.com/post/the-deadly-leptospirosis


Plague

Plague has been a disease of major concern during its outbreaks in yesteryears. It is a communicable disease transmitted to man by the bite of infected rat flea.Mainly a disease of rodents,it is a zoonoses of importance to man.Patients with diagnosis of suspected plague should be kept in strict isolation for 48 hour after initiation of specific therapy. In fact,Quarantine practices took off following plague outbreaks in sailors back in the 15th century.

You can read more about the interesting evolution of plague and quarantine practices in my blogpost at: https://www.scalpelstrokes.com/post/a-brief-history-of-quarantine


Yellow Fever

Yellow fever is a viral infection which is spread by mosquitoes(Aedes aegypti)and is seen endemic to regions of South America and Africa.It is also a lethal disease if not treated properly.However,single shot of yellow fever vaccine confers nearly 100% immunity and hence is mandatory for travellers to show vaccination certificate while travelling to these endemic areas.

Yellow fever has been dealt with in detail on my blogpost: https://www.scalpelstrokes.com/post/yellow-fever


Influenza

Human beings can be infected with zoonotic influenza viruses like avian or swine flu viruses.Recently we had a H1N1 outbreak in relation to this.Influenza may manifest as a mild upper respiratory infection(flu) but may also present with severe pneumonia leading to respiratory distress leading to ventilator dependence and death.Majority of infections have been linked to contacts with infected poultry. It is quite difficult to eradicate the reservoirs and hence outbreaks of epidemics are bound to happen.


Coronavirus

SARS(Severe Acute Respiratory Syndrome) or “atypical pneumonia”, was the first well documented Human Coronavirus pandemic in human history.The first case of SARS was reported in 2002 in Guangdong Province of China.The novel coronavirus announced its arrival in late 2019 when news regarding outbreak of a pneumonia-like illness in Wuhan province of China started pouring in.Huanan Seafood Wholesale Market was identified to be the source of outbreak.Severe symptoms and death was observed in the elderly and those with multiple co-morbidities. In March 2020,WHO declared COVID19 as a pandemic and even to this day,we are still in the grasps of this infectious disease.


Hydatid disease

Hydatid disease or cystic echinococcosis is caused by infection with the larval stage of a microbe called dog tapeworm.Humans get infected when they ingest the eggs or larva of the tapeworm prsesnt in faecal matter of infected animals accidentally.This after multiplication leads to cyst formation in many organs notably liver and lungs.Patients usually present with abdominal pain and on imaging,the diagnosi becomes evident.Surgical management is the definitive treatment.


Control and prevention of zoonotic diseases

Appropriate guidelines laid down in the rearing and breeding of domestic animals have to be diligently followed by all involved in it. Immunization of pets must be carried out strictly as per schedule.Waste disposal and burying of dead animals must be done as per protocol. Water sources are to be kept clean from contamination.Community spread can be minimized by routine handwashing after contact with animals as well as taking personal protective measures.Report to the veterinarian if you think your domestic animals are looking sick and isolate if needed.





July 6 is considered as 'World Zoonosis Day'. WHO has launched 'The One Health' programme for the control of zoonotic diseases by preventing the emergence of outbreaks and pandemics at a multisectoral level.


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